1. Field of the Invention
The present invention relates generally to the art of roller shades, and more particularly to an improved roller shade which includes a variable force braking feature to prevent the shade from self-lowering as shade material is unwound from the roller tube. In its most preferred embodiment, the invention also includes a lift assembly to assist in raising the shade.
2. Description of the Prior Art
Roller shades have been known for many years and are available for a wide variety of applications. Smaller shades may be used in residences, and much larger units are used for commercial applications, e.g., office buildings, hotels, restaurants, etc. Most prior art shades include mounting brackets for supporting opposed ends of a tube, around which the shade material is rolled. Many of the prior art shades also include some form of lift assist, usually a spring element which is wound when the shade is lowered and released when the shade is raised. In smaller units the lowering of the shade results in a noticeable increase in the force required, due to the action of the spring, and latching mechanisms (e.g., ratchet and pawl systems) are frequently employed to keep the shade in a desired position. When it is time to raise the shade, the latching mechanism is deactivated and the spring assists in raising the shade to either a full roll-up or to an intermediate location.
Different operational factors are involved in the design of commercial shades, mainly due to their larger size and to the heavier shade materials frequently employed. As the shade material is unrolled during the lowering step, it exerts a torque on the tube, and in many applications it is considerable. In the absence of some additional shade components, the weight of the unrolled shade material can result in undesirable free-falling. In a related aspect of these larger shades, the considerable weight of the unrolled shade material prevents the use of common lift assist springs and creates difficulty during shade raising.
Several U.S. patents address certain of the aforementioned characteristics of shade construction and use. For example, U.S. Pat. No. 4,535,830 issued Aug. 20, 1985 to Appel, et al. for "Lateral-Traction Roller Shade" discloses a stationary rod inside the shade cylinder and a retraction spring having an end secured to the rod. The other end rotates about the interior rod to act as a lift assist.
In U.S. Pat. No. 1,938,729 issued Dec. 12, 1933 to Traut for a "Spring Roller", a torsion spring is wound by a bushing with a key groove engaging a rib on the roller tube. The arrangement is said to materially reduce the frictional wear on the moving parts.
Robinson, in U.S. Pat. No, 1,591,104 issued Jul. 6, 1926 for "Window Shade Roller" discloses a threaded nut moving on a threaded rod between two friction discs. In this arrangement, a spring is compressed toward the nut to separate the discs and relieve the frictional pressure on a bracket.
Holt, et al., in U.S. Pat. No. 1,605,111 issued Nov. 2, 1926 uses a different mechanism in a "Shade Roller", i.e. one which employs a torsion spring having two ends. One end is anchored to the axle of the shade, while the other end is fixed to two devices which form a sliding, non-rotative bung engaged with a rib extending along the shade roller. The stored energy is apparently used to lift the shade, although the patent description is unclear.
On May 17, 1910, U.S. Pat. No. 958,605 was issued to Doring for an "Automatic Curtain Roller." In this device a traveling nut and a compressible spring are used in a roller shade. However, no friction mechanism is shown, and when the roller is fully lowered, its hem is secured by an eyelet engaging a peg or stud driven into the window casing. The spring which moves the traveling nut rotates the spindle of a roller (using toothed wheels), thereby winding or raising the curtain shade. The drive functions as a lift assist, rather than as a variable load braking device.
Finally, three patents have been issued to Berman, et al for "Window Shade Roller Assembly", namely U.S. Pat. No. 4,323,105 issued Apr. 6, 1982, U.S. Pat. No. 4,223,714 issued Sep. 23, 1980 and U.S. Pat. No. Re. 31,793 issued Jan. 8, 1985. In each of these patents a shaft passes through the drive mechanism and a spring is placed over the shaft to help insure proper positioning and operation of the mechanism. The spring forces exerted against the drive components also are said to prevent the roll from rotating and unwinding the shade which may occur due to the weight of a partially lowered shade.
While various types of lift assists and other spring systems are known in the art, none of them provide a desirable variable load braking capability, alone or in combination with a lift assembly. An improved shade which solves the above-noted problems with prior art shades and which features a variable load braking system which can be used in a stand alone fashion or combined with a lift assist, would represent a significant advance in this art.